Low-emission glass (Low-E) is a clear glass, it has a microscopically-thin coating of metal oxide. This allows the sun's heat and light to pass through the glass into the building. At the same time it blocks heat from leaving the room, reducing heat loss considerably.

 There are two types of Low-E (low emissivity) glass available:

• On-line coated (pyrolitic process): this is a clear glass which has been coated with a metal oxide through pyrolysis when the glass leaves the tin bath (at 650°C). The coating is therefore very resistant to mechanical damage, and this Low-E glass can be cut, tempered or laminated just as normal uncoated glass. This coating is also known as hard coating.
• Off-line coated (magnetron process): is a clear glass which has received, on one of its faces, a silver coating applied by magnetically-enhanced cathode sputtering. This type of Low-E must be used exclusively in insulating glass, with the coating on an internal face. It can be tempered and laminated.

Low-E glass is a type of insulating glass, which increases the energy efficiency of windows by reducing the transfer of heat or cold through glass. That means in the winter your house stays warmer, and in the summer it stays cooler.